Virtual reality simulator and method for small laboratory animals

ABSTRACT

The present invention relates to a virtual reality simulator (10) for small laboratory animals (100), in particular rodents, which comprises a head clamping mechanism (20) for securing the laboratory animal (100) and virtual reality glasses (40) with two wings (30), each of the wings (30) having a display (34) and a lens system (36) spaced therefrom and connected together by a light barrier cover (32), and the virtual reality glasses (40) are configured to allow the two wings (30) to align with each of the eyes (101) of the laboratory animal (100), respectively. The invention further relates to a method applying such a simulator (10).

The present invention relates to a virtual reality simulator for smalllaboratory animals, in particular rodents.

The invention further relates to a method for simulating virtual realityfor small laboratory animals.

Brain electrophysiological (EEG, electrode) and low-resolutionmicroscopic measurements used in neurobiological research can be easilyperformed on freely moving experimental animals (e.g., mice, rats). Incontrast, high-resolution in vivo brain imaging, such as two-photonmicroscopy occurs through a so-called craniotomy window in a head-fixedstate. However, this makes it more difficult to perform experimentswhere we want to study the interaction of the animal with itsenvironment and the resulting brain activity.

The solution to the above problem is the creation of a virtualenvironment (VR), which provides an opportunity to perform controlledanimal experiments with a fixed head. There are currently severalsolutions for implementing a virtual environment. A common feature ofthese is that the virtual image content is displayed on the walls of theroom surrounding the animal, such as using a projector or screen.Holscher et al. (Rats are able to navigate in virtual reality. J ExpBiol (2005); 208(3): 561-569) were the first to create the design thatis still the basis for most virtual environment system designed forrodent. The main elements of this are a properly designed visualstimulus display and a treadmill. In this solution, the animal issurrounded by a torus-shaped dome 140 cm in diameter and 80 cm high, onthe inner surface of which the virtual image content is projected bymeans of a projector. The animal stands inside the torus, on a sphere 50cm in diameter, the movement of which—through a sensor that detects themovement of the driven surface—changes the projected virtual environmentaround the animal. The advantage of this solution is that the projectedimage almost completely fills the animal's field of vision. Further,known developments focus on the key elements of this basic design. Forexample, a solution called “JetBall-Dome” by a company called Phenosysuses a spherical dome instead of a torus and “floats” the sphericaltreadmill without friction by flowing compressed air.

Although many of the behavioral parameters of the animal interactingwith its environment (e.g., running speed, eye movement, feeding, etc.)can be measured during in vivo brain imaging through the virtualenvironment systems described above, none of the known solutions provideadequate feedback on the animal's behavior and sensory stimulus. This isbecause these embodiments still do not fully create an immersive virtualenvironment (i.e., the level of perception of the virtual environment asif the animal were indeed present in the VR environment) due to a lackof depth, and due to the filling the binocular field with a continuoussurface (only one, 2-dimensional image is displayed). We recognized thatfor 2-dimensional visual content, even if it substantially fills theanimal's field of view, the laboratory animal finds enough visualreference points from its real environment. Because the animal's head isfixed, its vestibular system does not sense movement, and this isconfirmed by these visual “grips” in its field of view. As a result, theanimal does not believe it is moving, which can negatively affect theexperiment. A further disadvantage of the known solutions is that theyare not compatible with or ergonomically usable with multi-photon (e.g.two-photon) microscopes due to the large projection surfaces required tocover the field of view, as the dome can impede the free movement of themicroscope objective.

Due to the above disadvantages, the current solutions are only suitableto a limited extent for the creation of virtual environments forexperiments or for their combined use with two-photon microscopes.

It is an object of the present invention to provide a virtual realitysimulator and method for small laboratory animals which is free from thedisadvantages of the prior art solutions, i.e. which provides animmersive virtual environment for the fixed laboratory animal and whichis compatible with two-photon microscopes.

It was recognized that the main consideration in behavioral, visual, andlearning experiments is immersion, which can be achieved by depthperception as well as complete coverage of the field of view.

The invention is based on the recognition that with the help of avirtual reality simulator comprising compact virtual reality glasseswith a large field of view and binocular depth sensing developed forlaboratory animals, the laboratory animal (e.g. a mouse) can solve realbehavioral tasks during electrophysiological- or brain imaging. Thanksto the invention, the immersion is formed practically immediately, andthe experimental animal can realistically experience the virtualenvironment in a head-fixed state. This effect was experimentallydemonstrated in five animals, during which we were able to stop theanimal at the edge of a virtual abyss with high accuracy withoutteaching or accustoming to the system. When the virtual sidewalk wasextended, the animals continued to run. This proves that they stoppedbecause of 3-dimensional spatial perception, not just because of thecontrast difference. With a conventional monitoring system, the sameanimal was unable to locate the abyss due to a lack of immersion.

It was also recognized that by using the simulator and method of thepresent invention, the time required to learn in visual learningexperiments can be reduced surprisingly, by orders of magnitude comparedto prior art systems (from 1-2 weeks to a few days). It is also suitablefor examining the learning process, as we have already detected asignificant learning process within a 40-minute period. The simulatorand method according to the invention are also suitable for carrying outthe behavioral experiments described in the literature.

In accordance with the above recognition the task was solved with thesimulator according to claim 1 and with the method according to claim14.

The preferred embodiments of the invention are determined in thedependent claims.

Further details of the invention will be explained by way of exemplaryembodiments with reference to figures, wherein:

FIG. 1a is a schematic front perspective view of an exemplary embodimentof a simulator according to the invention in the condition applied tothe laboratory animal,

FIG. 1b is a schematic rear perspective view of the main parts of thesimulator shown in FIG. 1 a,

FIG. 2 is a perspective view of the simulator shown in FIG. 1a withoutwings,

FIG. 3 is a schematic sectional view of an exemplary embodiment of awing according to the invention,

FIG. 4 is a schematic diagram illustrating the creation of virtual imagecontent according to the invention.

FIG. 1 a shows a schematic front perspective view of an exemplaryembodiment of the simulator 10 according to the invention, in thecondition where the simulator 10 is applied to a small laboratory animal100. The simulator 10 is used to create a virtual reality for a smalllaboratory animal 100. Virtual reality (VR) is a 3-dimensionalartificial environment generated by a computing device in which elementsof reality are completely excluded. The animal 100 can “tour” thevirtual environment, interact with its elements. VR is thus the set ofvisual (or audio) information generated by a computer device thataffects the senses (primarily sight, but also hearing) of the animal 100as a result of the interaction between the animal 100 and the computerdevice. It is to be understood that in the context of the presentinvention, small laboratory animals 100 are primarily rodents (e.g.,mice, rats, rabbits), but the term animals 100 includes other smallanimals commonly used in laboratory experiments (e.g., monkeys, lizards,etc.), as will be apparent to those skilled in the art.

The simulator 10 of the present invention includes a head clampingmechanism 20 for securing the head of a laboratory animal 100 andvirtual reality glasses 40 with two wings 30. The head clampingmechanism 20 may preferably be made of metal or any material of suitablestrength suitable for securing the head of the animal 100, therebyholding the animal 100 in place. The head clamping mechanism 20 mayoptionally be formed of a single piece or may consist of several parts,for example fastened to each other by screws, as can be seen in FIGS. 1aand 1b . In a particularly preferred embodiment, the head clampingmechanism 20 includes an observation opening 22 for a microscopeobjective 210 through which craniotomy brain imaging, known to thoseskilled in the art, can be performed in vivo on the animal 100. The headclamping mechanism 20 partially or, if appropriate, completely delimitsthe observation opening 22 (see FIGS. 1 a, 1 b and 2).

Each of the wings 30 having a display 34 and a lens system 36 spacedtherefrom which connected together by a light barrier cover 32. Thedisplay 34 can be any type of display using known technology, such asLCD, OLED, etc., the resolution of which is suitable for creating avirtual reality experience. The resolution of the display 34 ispreferably at least full HD, more preferably at least 2K, as is known tothose skilled in the art. In an exemplary embodiment, the display 34 isa commercially available 2.9-inch diameter IPS LCD display with aresolution of 1440×1440 pixels. In a particularly preferred embodiment,the display 34 is designed as a bidirectional display 34 to monitor thepupil and eye movement of the experimental animal 100. In this case, thedisplay 34 also functions as a CMOS camera sensor, so that in additionto displaying the image, digital images can also be taken with thedisplay 34. Such a display 34 may be, for example, a 0.6-inch diameter,2K resolution OLED display from Fraunhofer FEP.

In the context of the present description, the term lens system 36 is tobe construed broadly to include an optical element comprising one or,where appropriate, multiple lens elements. The lens system 36 is sizedto image an associated display 34 on the retina of the laboratory animal100. Preferably, the lens system 36 is corrected for optical aberration(e.g., spherical, chromatic aberration) as will be apparent to thoseskilled in the art. Note that the lens system 36 may optionally be asingle member aspherical lens or a Fresnel lens for size reduction.

FIG. 3 is a schematic sectional view of an exemplary embodiment of thewing 30 showing a possible configuration of the display 34 and lenssystem 36 connected by the light barrier cover 32 and the arrangement ofthe wing 30 relative to the eyes 101 of the animal 100. The cover 32serves to secure the display 34 and the lens system 36 relative to eachother and defines an interior space between the display 34 and the lenssystem 36 isolated from the outside world. The cover 32 is at leastpartially solid walled. In terms of material, it may be made of, forexample, metal, plastic, etc., which provide adequate structuralstrength and light barrier, i.e., are suitable for securing the display34 and lens system 36 relative to each other and do not allow outsidelight into the interior delimited by the cover 32. In a preferredembodiment, at least a portion of the light barrier cover 32 is made ofa resilient material, preferably a light-blocking fabric. The functionof this will be explained in detail later. The design of the wing 30 issuch that the optical axis of the lens system 36 is preferablyperpendicular to the plane of the display 34.

The virtual reality glasses 40 of the present invention are configuredto allow the two wings 30 to align with one or the other eye 101 of thelaboratory animal 100, respectively, and are preferably secured to thehead clamping mechanism 20 by means of fasteners 50. When the simulator10 is mounted, one eye 101 of the animal 100 can see only the image ofone display 34, while the other eye 101 of the animal 100 can only seethe image of the other display 34. In a particularly preferredembodiment, the fastening elements 50 are designed as a mechanism, suchas a ball-and-socket mechanism, for allowing the individual wings 30 torotate about any axis and to move along at least one, preferablyvertically, axis. In this embodiment, the cover 32 of the wings 30 haveholes 38 into which socket 52 of the ball joint of the fastening element50 can be fastened. The ball joint socket 52 are fitted with ball heads54 with shafts 56, which ball heads 54 are freely rotatable in the balljoint sockets 52. The end of the shaft 56 opposite the ball head 54 isreleasably secured (e.g., by a screw) in a substantially verticallongitudinal bore 24 formed in the head clamping mechanism 20, as shown,for example, in FIGS. 1b and 2. In this way, the end of the shaft 56 canbe fixed in the desired position along the longitudinal bore 24, so thatthe height of the wing 30 relative to the head clamping mechanism 20 canbe adjusted. The advantage of the ball-and-socket mechanism is that thewings 30 can be aligned independently with the eyes 101 of the animal100, i.e., the optical axes of the lens systems 36 can be fittedseparately, exactly to the eye axes of the eyes 101, in paralleltherewith. Note that other securing methods than those described abovemay be considered.

In embodiments where the head clamping mechanism 20 includes an opening22, the wings 30 are secured to the head clamping mechanism 20 in amanner that leaves the observation opening 22 free, as shown, forexample, in FIG. 1a . In a particularly preferred embodiment, the wings30 are configured to allow the objective 210 of the microscope to befitted to the observation opening 22 when the wings 30 are mounted onthe head clamping mechanism 20. This can be ensured on the one hand bythe appropriate sizing of the wings 30 and on the other hand by theappropriate choice of the material of the cover 32. For example, anembodiment is possible in which portions of the covers 32 proximal tothe lens are made of a flexible, light-barrier textile or other flexiblelight-barrier material so that the lens 210 can be brought closer to theaperture 22 by deforming the fabric of the cover 32.

In the particularly preferred embodiment shown in FIG. 1a , the wings 30are dimensioned in such a way as to leave the mustaches of thelaboratory animal 100 free when the wings 30 are applied, i.e. the wings30 do not touch the mustache of the animal 100. This can be provided bychoosing the appropriate size of the display 34, depending on thespecies of animal 100. The advantage of this embodiment is that thesimulator 10 does not interfere with the tactile sensation of the animal100, thereby improving immersion and simulation efficiency.

In a particularly preferred embodiment, the simulator 10 comprises atread 60, preferably in the form of a treadmill, a rotating disc, or aspherical treadmill arranged under the head clamping mechanism 20 whichcan be movable by the laboratory animal 100, as is known to thoseskilled in the art. The tread 60 is positioned below the head clampingmechanism 20 in such a way that the animal 100 secured by the headclamping mechanism 20 stands on the tread 60. The animal 100, secured bythe head clamping mechanism 20, is able to mimic advancing motion bymoving the tread 60, similar to people running on a treadmill. In apreferred embodiment, the tread 60 is provided with one or moredisplacement sensors 62 to determine the simulated speed or direction oftravel of the animal 100.

The simulator 10 according to the invention preferably further comprisesa control unit 70 having at least one processor and a storage device, indata communication with the displays 34 and the sensor 62. The termcontrol unit 70 is to be construed broadly as used herein to include anyhardware device capable of receiving, processing, storing, andelectronically transmitting processed digital data. In a particularlypreferred embodiment, the control unit 70 is configured as a personalcomputer (e.g., a desktop or laptop computer) having a storage forstoring data received from the sensor 62 as well as computer programsand having a processor for processing the received data and runningcomputer programs. The control unit 70 may optionally include one ormore input devices (e.g., keyboard, mouse, etc.) in addition to theusual elements (e.g., direct access memory, network card, etc.) or mayinclude an interface to serve as both an output and an input device(e.g. such as a CD/DVD burner/reader, etc.) as will be apparent to thoseskilled in the art. By means of a data transmission connection betweenthe control unit 70 and the displays 34, which can take place, forexample, via a MIPI interface or HDMI, the data processed by the controlunit 70 can be transmitted to the display 34. Note that the dataconnection may be wired or, optionally, wireless (e.g., WiFi, Bluetooth,etc.), as is known to those skilled in the art.

The control unit 70 is configured to display the virtual image contenton the displays 34 corresponding to the fields of view detected by theeyes 101 of the laboratory animal 100 by executing the at least onecomputer program. In other words, the control unit 70 sends differentvirtual image content to the displays 34 in such a way that the righteye 101 and the left eye 101 of the animal 100 see a right image and adifferent left image respectively, according to the rules ofstereoscopic display, which the brain of the animal 100 perceives as asingle 3-dimensional image. For example, in the embodiment shown in FIG.4, the virtual object is a slice of cheese, the images of which aredisplayed on the displays 34 at different sizes, angles, and so on, asis known to those skilled in the art. Overlapping the fields of viewperceived by the eyes 101 of the animal 100 develops binocular vision(spatial sensation) and monocular vision in the other parts. Thisapproximately means (for example in case of mice) a 40-degree binocularand 270-degree peripheral field of view. As previously mentioned, whenthe simulator 10 is mounted, the optical axes of the lens systems 36 arepreferably parallel to the eye axes of the eyes 101. If this is notpossible (e.g. because the wings 30 need to be tilted better relative tothe eye axes to free up space for the objective 210 used to examine thelaboratory animal 100, or because the wings 30 cannot be tilted/rotatedin arbitrary direction), then in a preferred embodiment displaying a3-dimensional perspective-corrected virtual image content for thelaboratory animal 100 with the 34 displays in a manner known per se.Note that the virtual image content generated by the control unit 70during the running of the computer program may contain not only visualdata but also, if appropriate, audio data (audio track), hence imagedata and content also means video data containing both visual and audioelements. In an exemplary embodiment, the simulator 10 includes a soundgenerating unit (not shown) for generating sound, controlled by thecontrol unit 70, preferably a speaker for sounding the audio track ofthe virtual image content generated by the control unit 70. In anotherpossible embodiment, the virtual image content also includes haptic datathat has been transmitted to the animal 100 using devices designed forthis purpose (e.g., vibrating motors), as is known to those skilled inthe art.

In embodiments including the tread 60, the control unit 70 is preferablyconfigured to generate and send virtual image content to the displays34, taking into account the displacement measured by the one or moresensors 62. That is, for example, if the animal 100 simulates a straighttravel on the tread 60, the virtual image content will changeaccordingly as if the animal 100 were traveling straight in the virtualspace. For example, if the animal 100 moves the tread 60 as if it wereturning to the left, the generated virtual image content will alsochange as if the animal 100 had turned to the left in the virtual space.In a possible embodiment, the simulator 10 includes a locking means(e.g., a brake) for preventing the movement of the tread 60, by means ofwhich the tread 60 moved by the animal 100 can be stopped at the desiredtime so that the animal 100 cannot move it further. The locking means ispreferably designed to be operated by the control unit 70. Thus, if theanimal 100 reaches a virtual object (e.g. a wall) in the virtualenvironment during the simulation and wants to move forward, the tread60 can be stopped immediately by the locking means, so that the animal100 perceives, as in reality, that it cannot navigate through thevirtual object. Should the animal 100 move in the direction of bypassingthe virtual object, the tread 60 may be unblocked by releasing thelocking means so that the animal 100 can continue roaming the virtualenvironment. The locking of the tread 60 may be supplemented by othereffects (e.g., sound or haptic), making the simulation of the virtualenvironment even more realistic.

The invention further relates to a method for simulating virtual realityfor small laboratory animals. In the following, the operation of thesimulator 10 according to the invention will be described together withthe method according to the invention.

In a particularly preferred embodiment, the method according to theinvention is carried out by means of the simulator 10 according to theinvention described above. During the method, the head of the laboratoryanimal 100 is fixed by means of the head clamping mechanism 20. Theanimal 100 may be secured in any known manner, such as by gluing. Thehead clamping mechanism 20 is provided with two virtual reality glasses40 with wings 30, each of which is provided with a display 34 and a lenssystem 36 spaced therefrom, which connected together by a light barriercover 32. In a preferred embodiment, the glasses 40 are secured to thehead clamping mechanism 20 by the ball-and-socket mechanism shown above,by means of which the two wings 30 are adjusted to one or the other eye101 of the laboratory animal 100, respectively. When adjusting the wings30, care must be taken to ensure that the optical axes of the lenssystems 36 are as close as possible to the eye axes of the eyes 101 ofthe animal 100 and that the lens systems 36 are spaced from the eyes 101of the animal 100 to project images of the displays 34 onto the retinasof the animal 100. In order to create the best possible virtualexperience, the wings 30 are preferably designed to shield the spacebetween the eyes 101 and the lens systems 36 as well. Thus, the 100animals do not visually perceive anything from the outside world. Oncethe wings 30 have been adjusted, the displays 34 display virtual imagecontent corresponding to the fields of view of the laboratory animal100, i.e. slightly different from the perspectives of the two eyes 101,on the displays 34, which the animal's 100 brain perceives as a single3-dimensional image. The virtual image contents displayed on thedisplays 34, i.e. the computer program running on the control unit 70,are selected depending on the type of experiment to be performed. Forexample, if you want to perform a learning experiment with 100 animals,the virtual reality created by the virtual visual content can be, forexample, a virtual maze, and so on. In a particularly preferredembodiment, a tread 60, preferably a treadmill, a rotating disc, or aspherical treadmill, is provided under the head clamping mechanism 20 onwhich the laboratory animal 100 may perform running movements. Thedisplacement of the tread 60 is sensed by the one or more sensors 62,and the displays 34 display virtual image content corresponding to thesensed displacement. In other words, the virtual environment isgenerated according to the signals of the sensor 62, so that the animal100 feels that it is inside the virtual environment and can traverse it.

In a particularly preferred embodiment, an observation opening 22 isprovided on the head clamping mechanism 20 for a microscope objective210, and while simulating virtual reality, the brain activity of theexperimental animal 100 is measured through the observation opening 22using the microscope (e.g., a two-photon microscope). In thisembodiment, a craniotomy window is formed on the skull of the animal 100prior to securing the animal 100, as will be apparent to those skilledin the art. Brain processes can be examined through the opening 22 withthe help of the microscope, so that several behavioral parameters of the100 animals interacting with the virtual environment can be measured.The type of experiment can be modified by changing the virtualenvironment.

Since the virtual image content displayed on the displays 34 coverssubstantially the entire field of view of the animal 100, in order tomore accurately determine the animal's 100 interaction with the virtualenvironment, it is desirable to determine which part of the virtualenvironment the animal 100 is looking at. Therefore, in a preferredembodiment, a bidirectional display 34 adapted to monitor the eyemovement, and preferably the pupil movement of the laboratory animal 100is provided. From the measured eye movement and preferably pupilmovement data, visual directions are determined by means of which oneach display 34 the currently displayed image part or the virtual objectbelonging to the image part on which the animal 100 focuses at a givenmoment can be identified. For example, in a given experiment, it can bedetermined whether the animal 100 noticed a virtual object (e.g., food,predator, etc.) in the virtual environment that is important to theexperiment. In this way, the interaction of the animal 100 with thevirtual environment can be studied even more effectively.

With the aid of the simulator 10 and the method according to theinvention, it is possible to perform immediate effect experiments andsignificantly faster learning can be achieved compared to previousmethods. While using the prior art solutions, the visual learningprocess typically took 1-2 weeks, the simulator 10 and method of thepresent invention can reduce the time required to a time scale of up toa few days (e.g., 3-4 days). In the context of the present invention,learning a task means that the animal 100 is able to solve the task witha predetermined rate of success, e.g., can stably distinguish two typesof samples with at least 80% success. In our experiments, we found thatwith the help of the simulator 10 and method according to the invention,a significant success rate of 10-20% can be achieved even after 20-40minutes of use. That is, with the help of the simulator 10 and themethod, at least a superficial understanding of the task can be ensuredvery quickly. A further advantage is that, compared to other VRsolutions, there are no disturbing visual reference points outside thevirtual environment in the animal's field of view that would ruin thevirtual reality experience. Thus, the immersion is formed in the animal100 practically immediately after the glasses 40 are placed, in contrastto the prior art, where either there is no virtual reality experience atall, or it requires conditioning of the animal 100 for weeks. Theglasses 40 of the present invention provide binocular vision to theanimal 100, thereby providing perspective and depth for which prior artsystems are not suitable. A further advantage of the simulator 10 isthat it can be easily and flexibly adapted to the desired position ofthe animal 100 under the microscope, as well as to the current locationof the operation on the skull and the size of the animal 100. Thesimulator 10 is applicable to small laboratory animals 100 (e.g., mice,rats, marmosets) and is designed to be compatible with multi-photonmicroscopy and electrophysiological measurement procedures.

1. Virtual reality simulator (10) for small laboratory animals (100), inparticular rodents, characterized in that it comprises a head clampingmechanism (20) for securing the laboratory animal (100) and virtualreality glasses (40) with two wings (30), each of the wings (30) havinga display (34) and a lens system (36) spaced therefrom which connectedtogether by a light barrier cover (32), and the virtual reality glasses(40) are configured to allow the two wings (30) to align with each ofthe eyes (101) of the laboratory animal (100), respectively.
 2. Thesimulator Simulator (10) according to claim 1, characterized in that thevirtual reality glasses (40) are fixed to the head clamping mechanism(20) by means of fastening elements (50).
 3. The simulator (10)according to claim 1, characterized in that it comprises a control unit(70) in communication with the displays (34), having at least oneprocessor and a storage device, wherein at least one computer program isstored on the storage device, and the control unit (70) is configured todisplay virtual image content on the displays (34) corresponding tofields of view detected by the eyes (101) of the laboratory animal (100)by executing the at least one computer program.
 4. The simulator (10)according to claim 2, characterized in that the fastening elements (50)are provided as a mechanism for allowing the rotation of the individualwings (30) about any axis and for displacement of at least one axis. 5.The simulator (10) according to claim 1, characterized in that the lenssystem (36) comprises one or more lens elements and the lens system (36)is dimensioned to present display (34) to a retina of the laboratoryanimal (100) an image from display (34).
 6. The simulator (10) accordingto claim 1, characterized in that the display (34) is bidirectional formonitoring the pupil and eye movement of the laboratory animal (100). 7.The simulator (10) according to claim 1, characterized in that the headclamping mechanism (20) defines an observation opening (22) for amicroscope objective (210) and the wings (30) are fixed to the headclamping mechanism (20) in a manner leaving the observation opening (22)free.
 8. The simulator (10) according to claim 7, characterized in thatthe wings (30) are designed to allow the microscope objective (210) tobe fitted to the observation opening (22) when the wings (30) aremounted on the head clamping mechanism (20).
 9. The simulator (10)according to claim 1, characterized in that a part of the light barriercover (32) is made of a flexible material.
 10. The simulator (10)according to claim 1, characterized in that the head clamping mechanism(20) at least partially defines the observation opening (22).
 11. Thesimulator (10) according to claim 1, characterized in that the wings(30) are dimensioned to leave whiskers of the laboratory animal (100)free when the wings (30) are applied.
 12. The simulator Simulator (10)according to claim 1, characterized in that a tread (60) movable by thelaboratory animal (100) is provided below the head clamping mechanism.13. Simulator (10) according to claim 12, characterized in that thetread (60) is provided with a displacement sensor (62).
 14. A method ofsimulating virtual reality for small laboratory animals (100),comprising the steps of securing the head of the laboratory animal (100)with a head clamping mechanism (20), and providing virtual realityglasses (40) having two wings (30) on the head clamping mechanism (20),each of the wings (30) having a display (34) and a lens system (36)spaced therefrom which connected together by a light barrier cover (32),aligning the two wings (30) with the eyes (101) of the laboratory animal(100) respectively, and displaying virtual image content correspondingto the fields of view of the laboratory animal (100) on the displays(34).
 15. Method according to claim 14, characterized in that anobservation opening (22) for a microscope objective (210) is provided onthe head clamping mechanism (20) and during the simulation of virtualreality, the brain activity of the laboratory animal (100) is measuredby means of a microscope through the observation opening (22).
 16. Themethod according to claim 14, characterized in that a tread (60) isprovided below the head clamping mechanism (20), on which the laboratoryanimal (100) can perform a running movement, and movement of the tread(60) is detected by a sensor (62) and a virtual image contentcorresponding to the detected movement is displayed on the displays(34).
 17. The method according to claim 14, characterized in that abidirectional display (34) adapted to monitor the eye movement isprovided, pupil movement of the laboratory animal (100) is determined,during simulation of virtual reality, and parts of the virtual imagecontents are displayed on the displays (34) based on directions ofvision.
 18. The simulator (10) according to claim 2 wherein thefastening elements allow rotation of said individual wings (30) aboutany axis and for displacement of vertical axis.
 19. The simulator (10)according to claim 9 wherein the flexible material is a light blockingfabric.
 20. The simulator (10) according to claim 12 wherein the treadis a treadmill.